Analysis of the Wohltemperirtes Clavier shows that some of the fretting schemes for clavichords used in Bach's time permit performance of the work with approximately 179 voice-leading conflicts, of which five are difficult to perform and two impossible.
"Was the "Well-Tempered Clavier" Performable on a Fretted Clavichord?,"
Performance Practice Review:
1, Article 2.
Available at: http://scholarship.claremont.edu/ppr/vol5/iss1/2